A multispot satellite typically has a plurality of antenna spots instead of a single broad antenna spot. Each antenna spot covers a geographical zone or cell, and the plurality of antenna spots covers a plurality of contiguous geographical zones or cells. A multispot satellite allows several radiofrequency links to be established occupying the same frequency band on different antenna spots.
In the case of a high throughput satellite (HTS) telecommunication system, the satellite is used in a bidirectional manner, i.e. at the same time for:                relaying data emitted by a gateway towards a plurality of terrestrial terminals: this first link of the point-to-multipoint type constitutes the forward link FWD;        relaying data emitted by the plurality of terrestrial terminals towards the gateway: this second link of the multipoint-to-point type constitutes the return link RTN.        
An example of forward link FWD in a multispot configuration 1 is illustrated in FIG. 1. Radiofrequency signals are sent towards a multispot satellite 3 on an uplink LM by a gateway 2 connected to an internet backbone 5. Each of the radiofrequency signals is relayed at the level of the multispot satellite 3 and then transmitted on a downlink LD in the form of a plurality of spots. Each spot of the plurality covers an elementary covering zone, designated cell, of a plurality of cells. A plurality of terrestrial terminals is typically situated in each elementary covering zone, or cell. In the particular example of FIG. 1, the plurality of spots comprises eight spots SP1 to SP8, and the plurality of cells comprises eight cells C1 to C8. In the particular example of FIG. 1, the eight cells C1 to C8 associated respectively to the eight spots SP1 to SP8 form a group of cells served by the same gateway 2.
The return link RTN from the terrestrial terminals 6 towards the gateway 2 functions in an identical manner with an inverse direction of communication.
A HTS telecommunication system is typically focused on a bent-pipe transponder configuration, where the radiofrequency signals emitted on the uplink LM by the gateway 2 are demultiplexed and high power amplified on-board the satellite 3, and finally transmitted on the downlink LD.
The coordination of the frequencies between operators is carried out within the framework of a regulation decreed by the International Union of Telecommunications (IUT): thus, by way of example, the Ka band for Region 1 (Europe, Africa, Middle East) is defined in Table 1 below:
ForwardUplink, from the gateway towards the27.5 GHz to 30 GHzlinksatelliteDownlink, from the satellite towards the19.7 GHz to 20.2 GHzterrestrial terminalsReturnUplink, from the terrestrial terminals29.5 GHz to 30 GHzlinktowards the satelliteDownlink, from the satellite towards the17.7 GHz to 19.7 GHzgateway
Other bands such as Ku band can likewise be used.
Configuration 1, as described in FIG. 1, uses a technique designated frequency re-use: this technique allows the same range of frequencies to be used several times in the same satellite system so as to increase the total capacity of the system without increasing the attributed bandwidth.
Frequency re-use schemes are known, designated colour schemes, making a colour correspond to each of the spots of the satellite. These colour schemes are used to describe the attribution of a plurality of frequency bands to the spots of the satellite with a view to radiofrequency transmissions to be realized in each of these spots. In these schemes, each colour corresponds to one of these frequency bands.
Multispot satellites also allow polarised transmissions to be emitted and received. The polarisation can be linear or circular. When the polarisation is linear, the two directions of polarisation are respectively horizontal and vertical. When the polarisation is circular, the two directions of polarisation are respectively circular left and circular right. In the particular example of FIG. 1, the uplink LM leaving the gateway 2 uses two polarisations with four slots for each polarisation, respectively Ch1 to Ch4 for the first polarisation and Ch5 to Ch8 for the second polarisation. The use of two polarisations allows the total number of gateways to be reduced. The eight slots Ch1 to Ch8, after processing by the payload of the multispot satellite 3, will form the eight spots SP1 to SP8, one slot being associated with one spot in the example of FIG. 1.
A common approach to provide a given capacity on a forward link FWD of a high throughput satellite (HTS) telecommunication system while minimizing the number of needed gateways of the HTS telecommunication system consists in increasing the uplink bandwidth per gateway. For example, Ka-Sat gateways were designed to uplink 1.25 GHz per polarization, using five slots of 250 MHz each. Other future Ka-band HTS gateways were designed to uplink 2.5 GHz per polarization in the 27.5 GHz-30 GHz Ka frequency band, corresponding to the maximum allowable bandwidth in the uplink of the forward link in Ka band.
To further reduce the number of gateways and/or increase the maximum delivered capacity of the HTS telecommunication system, another approach is now to move towards higher frequency bands, such as V band in the frequency range 40 GHz-75 GHz, and W band in the frequency range 75 GHz-110 GHz.